Alkylthiosulfenyl dithiocarbamates as vulcanization accelerators



Patented Feb. 26, 1952 ALKYLTHIOSULFENYL DITHIOCARBAM- ATES AS VULCANIZATION ACCELER- ATORS Chester M. Hlmel, Palo Alto, Calif., and Lee 0.

Edmonds, Bartlesvilie, kla., assignors to Phillips Petroleum Company, a corporation of Delaware No Drawing. Application June 20, 1949, Serial No. 100,293

18 Claims. 1

This invention relates to the vulcanization of rubberlike materials. In one aspect this invention relates to the vulcanization of natural rubber. In another aspect this invention relates to the vulcanization of synthetic rubbers. In a particular aspect this invention relates to the use of new and improved accelerators in vulcanization. This invention also relates to improved vulcanized products. This application is a continuation-inpart of our copending application, Serial No. 59,- 025, filed November 8, 1948, now Patent No. 2,572,845.

Accelerators for the vulcanization of rubber, both natural and synthetic, vary greatly in the rate of vulcanization produced, and the degree of cure that is attained. Accelerators used heretoi'ore have either produced low rates of cure or, when high rates result, the product is susceptible to scorching or detrimental effects unless the temperature and other factors afiecting cure are critically controlled. Moreover, many of the accelerators, especially those attaining high rates of cure, are sufilclently expensive to introduce a serious factor of cost into a highly competitive field.

We have now discovered a series of vulcanization accelerators which provide vulcanizates of preferred physical properties, reduce the curing time to a low minimum, and effect a high degree of economy, both from their low cost of produc- 'tion,- and the usually small quantities required for optimum effect. The accelerators of our invention comprise alkylthiosulfenyl dithiocarbamates. These compounds may be produced by any means, but preferably by the interaction of an alkylthiosulfenyl halide containing not more than 16 carbon atoms per molecule with an alkali metal salt of an N-substituted dithiocarbamic acid according to the process disclosed in our copending application, Serial No. 59,025, filed November 8, 1948.

An object of this invention is to vulcanize rubber.

Another object of this invention is to produce a vulcanized rubber.

A further object of this invention is to produce rubber vulcanizates of superior physical characteristics.

Still another object of our invention is to effect a high rate of vulcanization of rubber.

A still further object is to provide selected,

wherein each R is selected from the group consisting of hydrogen, hydrocarbon radicals, and radicals which together with the nitrogen form a heterocyclic ring, but with not more than one R being hydrogen, and R is an alkyl radical. Preferably the total number of carbon atoms in the combined Rs is not more than 20, and in R is not more than 16. There are two parts 01'' the thiosulfenyl dithiocarbamate molecule which can be varied, the RzN-group and the -SSR' group. The nature of the RzN-group is of major significance while the SSR' group has much less eilect as long as R is an alkyl group. Most alkylthiosulfenyl dithiocarbamates wherein neither R is hydrogen give very satisfactory results as vulcanization accelerators, while those wherein one B is hydrogen, are generally less effective. However, compounds wherein one R is hydrogen should not be excluded from the scope of the invention, in its broadest forms. In addition to the structure of the RzN-group, it appears that the molecular weight has an effect on the activity. A compound wherein each R. is ethyl, or n-propyl is usually best suited for our purposes.

The amount of accelerator employed will vary, depending among other factors, upon the R2N- group and upon the SSR' group in the compound. The amount of accelerator used will generally be in the range between about 0.05 and about 5 parts, by weight, per 100 parts of rubber, with the amount usually ranging from 0.1 to 2 parts. When neither R is hydrogen, such as when each R is methyl, ethyl or n-propyl, the amount of accelerator required to produce the desired state of cure is much less than that necessary when R2N- is a heterocyclic ring such as in a morpholine or a piperidine thiosulfenyl dithiocarbamate. Thiosulfenyl dithiocarbamates containing a (CHs)zN- and an SSR' group in which R is ethyl, isopropyl or tertbutyl show only slight differences in activity. Each is an exceptionally active accelerator. The accelerator compounds of our invention, in which R. is tert-butyl are especially preferable since they exhibit an especially high degree of stability. Our most preferred compounds are those in which R contains from 4 to 7 carbon atoms. Typical of the accelerator compounds of our invention are N,N dimethyl S tert butylthiosulfenyl di thiocarbamate,

(CH3) zNC (S) SSS-t-CJ'IQ N,N diethyl S tert butylthiosulfenyl dithiocarbamate,

(Cal-Ia) zNCk'S) SSS-t-C4Ho N,N di n propyl S tert butylthiosulfenyl dithiocarbamate,

Piperidine S tert butylthiosulfenyl di-thiocarbamate,

CHI-CHI C 1 NC (8)555-t-C4Hl CHr-C I Morpholine S tert butylthiosulfenyl dithiocarbamate,

and N,N diethyl S tert octylthiosulfenyl dithiocarbamate.

(CzHs) :NC (S) SSS-t-CoHi'r Other alkylthiosulfenyl dithiocarbamates of interest are those containing a branched SSR' group such as SS-tert-amyl, -SS-tert-heptyl, and SS-tert-dodecyl.

The quantity of alkylthiosulfenyl dithiocarbamate accelerator employed will vary, depending on the compounding recipe employed, the particular alkylthiosulfenyl dithiocarbamate used,

the properties of the vulcanizate desired, and the like. However, in general we have found that in many instances the quantity will be substantially less than ordinarily employed with conventional type accelerators heretofore used such as, for example, the widely used N-cyclohexyl-2- benzothiazolesulfenamide.

As is indicated from the discussion and disclosure contained herein, except for the use of our novel\ vulcanization accelerators, and various eifects directly resulting therefrom, other factors of the practice of our invention are in accordance with vulcanization procedures well known to those skilled in the art. The actual vulcanization agent is usually sulfur, which is intimately admixed with the raw rubber in amounts between about 0.5 and 15 parts, based on 100 parts of rubber. The mixture to be vulcanized will also usually contain a substantial amount of carbon black and small amounts of a softener, such as asphalt, and a material, such as zinc oxide. Such components, and their proportions, are very familiar to those skilled in the art, and although the actual species and amounts of such materials which may be used in any particular instance will depend to a large extent upon the ultimate use for the vulcanized product, their determination, per se, is well within the ordinary skill of the available technical worker. This invention has been successfully applied to natural rubber and to various synthetic rubbers, particularly those which are unsaturated, such as are produced in whole or in part, from a conjugated diolefin, as 1,3-butadiene and its homologues and analogues, chloroprene and its homologues and analogues. etc.

Advantages of this invention are illustrated by the following examples. The reactants and their proportions and the other specific ingredients of the recipe are presented as being typical and should not be construed to limit the invention unduly.

Spent, furnace-type, high modulus carbon black.

Four different accelerators were employed, namely, N,N-dimethyl-S-tert-butyl thiosulfenyl dithiocarbamate, piperidine-S-tert-butyl thiosulfenyl dithiocarbamate, benzothiazyl disulfide, and 2-mercaptobenzothiazole, the latter two being used for comparative purposes. The mixes were milled and cured for varying lengths of time at 307 F. Stress-strain properties, measured at 80 F. for the cured rubbers are tabulated immediately below.

[35 per cent deflection for 2 hours at 212 F. plus 1 hour relaxation at 212 F.]

Example 1.--Stre3s-strain properties at 80 F.

Comparison at 15 Per Comgesslon Set at 30 Minutes oven Aged 24 Ham at mlmm Search M011- 300 P51- Elonga- Resll- 300 Per 151011115- Reall- Minute M ey M33311. 13'9" 1 5' 3'3? M5331... 533 it? 33? 0 I o 5 I Value p. a. l. Cent Cent p. s.l Cent Cent N, N-dimethyl-S-tert-butylthiosullenyl dithiocarbamate 0. 95 7 2, 200 3, 250 420 61 2, 900 310 65. 5 plperldlne-S-tert-butylghiosiilgenyl dlthloear- 12 9 7 31110 4 2,400 3 170 380 61 3,050 280 67.6 benzothlaz ldlsulfide..... 1.8 8+ 46 2, 200 3:080 400 63 2, 980 280 68.0 2-mercapto nzothnazola. 2.0 5+ 48 1,700 ,810 440 58 2,700 295 %.0

1 Parts per hundred parts of rubber. Compression set data are tabulated as follows. EXAMPLE 2 Twelve batches of natural rubber (smoked sheet) were compounded according to the foll refine Parts by weight Natural rubber 100 P e$ omprgsghgnet gi gdg 2 u urea n 0 e Accelerator PHR' u stegric a 01 d 3 10 Asphalt softener 6 Sulfur 2.5 1?" $13 53:5 53:3 3:3 2:3 2:2 Phenyl'beta'naphthylamine zg g ggf gg 1.5 44.0 12.8 7.7 5.0 3.0 so Accelerator variable Aspecial.furuact-i-type,high modulus carbon black. ipefldine s tert butyl 0.5 75.3 51.9 41.5 23.8 11.4 P dim? 1.0 86.1 30.0 17.5 3.8 5.1 Two different accelerators were employed, 1.5 51.0 10.3 9.8 5.8 3.5 1 an 55104111555. 10 4M 1M M name y, 1me y rtiary utyl osul- 0.5 57.5 40.4 20.0 10.7 12.1 fenyl dithiocarbamate and mercaptobenzothia- 05112501152 1 31501055-- 25 3 u zole. the latter being used for comparative purgg .3 132, 5.3 poses. Four batches of the rubber stock conz-mercaptobeniothia- 110 5411 3717 2411 15:2 815 taming variable quantltiei of each aqcelerawr 1015. 1.5 531 370 22.5 14.2 7.4 were compounded. The mlxes were milled and cured for varying lengths of time at 307 F. Re-

sults of evaluation tests on the cured rubbers 1 Parts per hundred parts of rubber. are h t presented Stress-strain properties at 80 F.

I Com- Scorch Min. 3007 Elonga- Reslh- Amlemmr PHR1 (me at Modufus, g s tion, ence, 522 3: i 307 F. p. s. i. Percent Percent 5 R 10 370 3, 130 510 48 s 20 1, 020 2, 770 555 35. 2 0.2 30 1,030 2,530 515 55.4 31.1 3.5 45 1,000 2,220 400 27.8 750 1,070 520 28.0 10 1,300 3. 730 510 44. 7 20 1,330 3, 510 575 32.4 0.4 30 1,340 3,420 570 58.4 25.5 2.75 45 1, 2, 590 535 24. 0 N,N-dimethyl-S- 75 550 1,300 550 21.3 tertiary-butyl- 10 1, 550 3, 950 580 43. 5 thiosullenyl di- 20 1,590 3,750 540 27.7 55155515501555 0.0 30 1,450 3,330 535 09.3 13.5 2.75

45 000 2,500 525 12.3 75 850 2,100 520 12.8 10 1, 800 4, 220 550 30. 0 20 1, 530 3, 570 535 14. 1 1.0 30 1,540 3,400 530 70.0 0.4 2.5 45 1,450 3,110 520 8.0 75 1,270 2,340 515 53 10 840 2,500 500 54.5 20 1,250 3,110 540 43.2 0.2 30 1,310 2,720 400 53.0 32.5 2.5+ 45 1,330 2,750 500 24.2 75 1, 2, 375 400 14. 4 10 1, 220 3, 370 577 55. 5 20 1, 520 3, 530 535 35. 3 0.4 30 1,570 3,530 535 72.5 22.7 2.25 45 1,470 3,410 535 1 14.5 Merceptobenzo- 75 1, 330 3,120 520 9. 5 511152515 10 1, 400 3, 550 500 50. 5 20 1,550 3,450 525 30.4 00 30 1,570 3.500 525 72.8 17.4 2.25-

| Parts per 100 parts of rubber.

A measure of ltate 0! euro. Low compression set values indicate more complete cure.

7 mum s The vulcanization accelerating activity of N,N- dimethyl-S-tert-butylthiosulfenyl dithiocarbamate was investigated at vulcanization temperatures of 280 and 260 F. and compared with those of mercaptobenzothiazole, as control. The compounding recipe of Example 1 was employed. Varied amounts of both the control compound and the novel accelerator compound were used.

Evaluation data were determined at approximately equivalent states of cure as measured by compression set values. The following tabulation is a summary of the results obtained.

1 Parts per hundred parts oi rubber.

40 Per Cent Compression Set, 30 Min. Cure, 260 F.

'r 11 11 en one 0 on PERI Modulus, p.s.i. Per 1;, p. s. i. Cent N N-dimethy-S-tertlar utyithiosulienyl ithiocarbamate 0. 8 l, 910 4, 640 660 Mercaptobenzothiazole... l. 0 l 590 4, 230 570 1 Parts per hundred parts oi rubber.

The alkylthiosulfenyl dithiocarbamate shows no loss in activity at these temperatures, 1. e., 260 to 280 R, which are lower than those of Example EXAMPLE 4 Natural rubber (smoked sheet) was compounded in accordance with the recipe oi. Example 2. N,N-dimethyl-S-tert-buty1thiosulfenyl dithiocarbamate, piperidine-S-tert-butylthiosulfenyl dithiocarbamate, benzothiazyl disulflde, and 2-mercaptobenzothiazole were employed as accelerators, the latter two being used for comparative purposes. The mixes were milled and cured ior varying lengths of time at 307 F. Stress-strain properties measured at 80 F., for the cured rubbers are tabulated as follows.

Stress-strain properties at 80 F.

Scorch Minimum 300 Per Cent Tensile Elon ation Resilience Accelerator PHR 1 Minutes Mooney Modulus, g

at a R value p. D. s. 1. Per Cent Per Cent COMPARISON AT PER CENT COMPRESSION SET AT 'MINUTES A'I 307 F.

N.N-dirnethyl-S-tcrt-butylthi0suli'enyi dithiocarbamate 0. 4 8+ 47 l, 380 3, 330 545 71. 3 pigeridme-S-wrt-butylthiosulienyi dithiocararnaie 4 8 53 l, 590 3, 630 565 69. 9 benzothiazyi d1sulflde 0. 4 9 55 1, 580 3, 550 530 72. 9 2-mercaptobenzothiazolc 0- 7 60 i, 580 3, 340 525 72. 5

COMPARISON AT PER CENT COMPRESSION SET AT 10 MINUTES AT 307' F.

N,N-dimcthyl-S-tert-butylthiosul[en yi dithiocarbamate v 0- 4 8+ 47 1, 390 3, 730 piReridinc-S-tert-butylthiosuli'enyl dithiocar- I amnh 0. 8 7+ 52 1, 980 4, 000 benzothiazyl disulilde 0.9 9 55 l, 800 4, 000 2-mereaptobenzoth1azoie 0. 7 5+ 62 l, 850 3, 950

. 1 Parts per hundred parts oi rubber.

Compression set data for these'cured rubbers are tabulated as follows. 17 Per Cent Compression Set, Compression set data 150 Min. Cure, 260 F. [35 per cent deflection for 2 hours atF2]l2 F. plus 1 hour relaxation a 300 Per Elon a- Cent Tensile tion PerCent Compression Set Modulus, p. s. 1. Per Minutes Cure at 307 F.

p. s. 1. Cent Accelerator PHR 1 N,N- dimethyl S tertiary butyithiosulienyl dithiocarbamate. 0.4 1,730 3,740 505 N'N dimethyl-s tert 3 Meroaptobenzoth1azole. 0.4 1,880 3, 890 490 but lthio ulf l 1 1-7 7-2 13.4 dlthiocarbamate. Parts per 100 parts rubber. plperidine s tert butyl thiosulfenyl dithiocarbamate' 131.6 8.4 7.3 012 28 Per Cent Compression Set 3 6 5 0 30 Min. Cure, 280 F. R5 benzothiazyl disulilde g3 52.8 7.0 414 2. .5 19.4 11.0 8 Tensile Z-mercaptobenzothia- 0.5 46.5 20.7 17.9 12.1 7.8 PHR zole. 0.6 42.7 21.8 14.5 9.5 6 1 Modulus, p. s. i. Per

DSJ' Cent 1.0 36.3 16.2 10.4 7.5 5.9

N N d th S t Parts per hundred parts of rubber.

, ime y erbunglmiosulfenyl 0 6 0 AS be evldent, to thOse Skilled In the art, 1 local flmaie- 1 4,100 510 various modifications of this invention can be Mercaptobenzothiazole. 1.0 1,540 3 920 540 made, or followed, in the light of the foregoing 1 Parts per hundred ports of rubber.

disclosure and discussion without departing from 76 the spirit or scope of the disclosure or the claims.

We claim:

1. The process of claim 10 wherein said substance comprises a polymer of a conjugated diolefin.

2. The process of claim 10 in which said accelerator is an N,N-dialky-S-tert-alkylthiosulfenyl dithiocarbamate.

3. The vulcanized substance resulting from the process of claim 10.

4. The product of vulcanization of natural rubber which has been vulcanized with sulfur in the presence of 0.05 to 5 parts, by weight, per 100 parts by weight of said natural rubber, of a vulcanization accelerator compound of the formula wherein each R is of the group consisting of hydrogen, hydrocarbon radicals, and radicals which together form a divalent radical selected from the group consisting of alkylene and oxaalkylene, said divalent radical forming a heterocyclic ring with the nitrogen, but with not more than one R being hydrogen, and wherein R is an alkyl hydrocarbon radical.

5. The product of vulcanization of natural rubber which has been vulcanized with sulfur in the presence of 0.05 to 5 parts, by weight, per 100 parts of said rubber, of N,N-dimethy1-S-tertiarybutylthiosulfenyl dithiocarbamate as a vulcanization accelerator.

6. A composition comprising a rubber copolymer of butadiene and styrene with sufiicient sulfur for vulcanization and with 0.05 to 5 parts, by weight, per 100 parts of rubber, of N,N-dimethyl-S-tert-butylthiosulfeny1 dithiocarbamate intimately admixed therewith.

7. An improved process for vulcanizing with sulfur a butadiene-styrene copolymer synthetic rubber,-which comprises admixing with such a synthetic rubber as a vulcanization accelerator an N ,N dialkyl S alkylthiosulfenyl dithiocarbamate, where the total number of carbon atoms in the dialkyl is not greater than and in the alkyl is not greater than 16, in an amount between 0.05 and 5 parts, by weight, per 100 parts of rubber, and vulcanizing the resulting rubber-accelerator admixture.

8. An improved process for vulcanizing natural rubber with sulfur which comprises admixing with said natural rubber as a vulcanization accelerator an N,N-dialkyl-S-alkylthiosulfenyl dithiocarbamate, where the total number of car-- bon atoms in the dialkyl is greater than 20 and in the alkyl is not greater than 16, in an amount between 0.05 and 5 parts by weight per 100 parts of rubber, and vulcanizing the resulting rubberaccelerator admixture.

9. The process of claim 8 wherein the accelerator is N,N-dimethyl-S-tert-butylthiosulfenyl dithiocarbamate.

10. An improved process for vulcanizing a sulfur-vulcanizable organic plastic substance containing unsaturated carbon to carbon bonds, with sulfur, which comprises admixing with such a substance to be vulcanized, as a vulcanization accelerator and in an amount between 0.05 and 5 parts by weight, per 100 parts by weight of said substance, a compound of the formula wherein each R is of the group consisting of hydrogen, hydrocarbon radicals, and radicals which together form a divalent radical selected from the group consisting of alkylene and oxaalkylene, said divalent radical forming a heterocyclic ring with the nitrogen, but with not more than one B being hydrogen, and wherein R is an alkyl hydrocarbon radical, and vulcanizing the resulting organic plastic substance-accelerator admixture.

11. The process of claim 10 wherein said accelerator is morpholine-S-tert-butylthiosulfenyl dithiocarbamate.

12. The vulcanized substance resulting from the process of claim 11.

13. A composition comprising a synthetic rubber copolymer of butadiene and styrene with sufficient sulfur for vulcanization and with 0.05 to 5 parts by weight, per parts by weight of said copolymer, of a vulcanization accelerator compound having the structural formula wherein each R is of the group consisting of hydrogen, hydrocarbon radicals, and radicals which together form a divalent radical selected from the group consisting of alkylene and oxaalkylene, said divalent radical forming a heterocyclic ring with the nitrogen, but with not more than one R being hydrogen, and wherein R is an alkyl hydrocarbon radical.

14. A composition comprising natural rubber together with suflicient sulfur for vulcanization and with 0.05 to 5 parts "by weight, per 100 parts by weight of said natural rubber, of piperidine-S- tert-butylthiosulfenyl dithiocarbamate.

15. An improved process for vulcanizing natural rubber with sulfur which comprises admixing with said natural rubber as a vulcanization accelerator, from 0.05 to 5 parts by weight of piperidine S tert butylthiosulfenyl dithiocarbamate per 100 parts by weight of said natural rubber, and vulcanizing the resulting rubber-accelerator admixture.

16. An improved process for vulcanizing a butadiene-styrene copolymer'synthetic rubber with sulfur which comprises admixing with such a synthetic rubber as a vulcanization accelerator from 0.05 to 5 parts by weight of piperidine-S- tat-butylthiosulfenyl dithiocarbamate per 100 parts by weight of said rubber, and vulcanizing the resulting synthetic rubber-accelerator admixture.

1'7. A composition comprising a rubber copolymer of butadiene and styrene with sufficient sulfur for vulcanization and with 0.05 to 5 parts by weight of piperidine S tert butylthiosulfenyl dithiocarbamate per 100 parts by weight of said copolymer.

18. An improved process for vulcanizing a synthetic rubber butadiene-styrene copolymer with sulfur, which comprises alnixing with such a synthetic rubber as a vulcanization accelerator from 0.05 to 5 parts by weight of N,N-dimethyl- S-tert-butylthiosulfenyl dithiocarbamate, per 100 parts by weight of said rubber, and vulcanizing the resulting synthetic rubber-accelerator admixture- CHESTER M. HHVIEL.

LEE 0. EDMONDS.

No references cited. 

10. AN IMPROVED PROCESS FOR VULCANIZING A SULFUR-VULCANIZABLE ORGANIC PLASTIC SUBSTANCE CONTAINING UNSATURATED CARBON TO CARBON BONDS, WITH SULFUR, WHICH COMPRISES ADMIXING WITH SUCH A SUBSTANCE TO BE VULCANIZED, AS A VULCANIZATION ACCELERATOR AND IN AN AMOUNT BETWEEN 0.05 AND 5 PARTS BY WEIGHT, PER 100 PARTS BY WEIGHT OF SAID SUBSTANCE, A COMPOUND OF THE FORMULA 